1. CONTENTS
What Is Bridge???
Types of Bridges
Arch Bridge
Beam Bridge
Cable-stayed Bridge
Cantilever Bridge
Truss Bridge
Suspension Bridge – An Introduction
Terms related to Suspension Bridge
Structural Analysis
Structural Failure
Quality Control in Suspension Cable
Advantages & Limitations
Load Distribution in Different Types of Bridges
Conclusion
References
2. BRIDGE
A bridge is a structure built to span a valley, road,
body of water, or other physical obstacle, for the
purpose of providing passage over the obstacle.
Designs of bridges vary depending on the function
of the bridge and the nature of the terrain where the
bridge is constructed.
3. TYPES OF BRIDGE
There are six main types of bridges:-
Arch Bridge
Beam Bridge
Cable-stayed Bridge
Cantilever Bridge
Truss Bridge
Suspension Bridge
4. ARCH BRIDGE
Arch bridges are arch-shaped and have abutments at each
end.
An arch bridge doesn't need additional supports or cables. In
fact it’s the shape of the structure that gives it its strength.
Arch bridges are designed to be constantly under
compression.
The weight of the bridge is thrust into the abutments at either
side.
Usually they are made for short span range but often set end-
to-end to form a large total length.
5. BEAM BRIDGE
Beam bridges are the simplest kind of bridge today.
Bridges consist of one horizontal beam with 2 supports
usually on either ends.
It is frequently used in pedestrian bridges and for highway
overpasses & flyovers.
They are constructed for short span requirements.
The weight of the bridge and any traffic on it is directly
supported by the piers.
The top side of the deck is under compression while the
bottom side of the deck is under tension.
To increase the bridge’s strength designers introduce truss to
the bridge’s beam.
6. CABLE-STAYED BRIDGE
A bridge that consists of one or more pylons with cables.
There are two major classes of cable-stayed bridges such as a harp
design & a fan design.
The cable-stay design is best suited for a medium span range.
The towers form the primary load-bearing structure.
It has greater stiffness.
The cables act as both temporary & permanent supports to the
bridge-deck.
The tower in a cable-stayed bridge is responsible for absorbing and
dealing with the compression forces while the cables are under
tension.
fan design harp design
7. CANTILEVER BRIDGE
A bridge built using cantilevers, structures that project
horizontally into space, supported on only one end.
For small footbridges, the cantilevers may be simple beams;
however, large cantilever bridges are designed using trusses.
These are constructed for short to medium span ranges.
Cantilevers support loads by tension of the upper members &
compression of the lower ones.
8. TRUSS BRIDGE
A bridge composed of straight connected elements which may
be stressed from tension, compression, or sometimes both in
response to dynamic loads.
A truss bridge is economical to construct owing to its efficient
use of materials.
These are usually constructed for short to medium span
range.
In India truss bridges are generally constructed for rail traffic.
Vertical members are in tension, lower horizontal members in
tension, shear, and bending, outer diagonal and top members
are in compression, while the inner diagonals are in tension.
9. SUSPENSION BRIDGE
Nowadays these are the pioneers in bridge technology.
Of all the bridge types in use today, the suspension bridge
allows for the longest span ranging from 2,000 to 7,000 feet.
This type of bridge has cables suspended between towers &
the cables support vertical suspender cables that carry the
weight of the deck below. This arrangement allows the deck to
be level or to arc upward for additional clearance.
The suspension cables are anchored at each end of the
bridge.
They are ideal for covering busy waterways.
10. TERMS RELATED TO SUSPENSION BRIDGE
Side span: segment between two pylons at the ends of a bridge.
Centre span: segment between two pylons at the centre of a bridge.
Side pylon: tower-like vertical construction situated at the side.
usually supporting the cables of a suspension bridge.
Foundation of a pylon: very durable lower part of a tower.
Suspender: support cable.
Suspension cable: set of braided wire that supports a bridge.
Pylon: tower-like vertical support that usually supports the cables of
a suspension bridge or a cable-stayed bridge.
Stiffening girder: tightener beam.
11. STRUCTURAL ANALYSIS
The main forces in a suspension bridge are tension in the
main cables and compression in the pillars. Since almost all
the force on the pillars is vertically downwards and they are
also stabilized by the main cables, they can be made quite
slender.
In a suspended deck bridge, cables suspended via towers
hold up the road deck. The weight is transferred by the cables
to the towers, which in turn transfer the weight to the ground.
Most of the weight or load of the bridge is transferred by the
cables to the anchorage systems. These are imbedded in
either solid rock or huge concrete blocks. Inside the
anchorages, the cables are spread over a large area to evenly
distribute the load and to prevent the cables from breaking
free.
13. STRUCTURAL FAILURE
Some bridges have in the past suffered from structural failure
due to combination of poor design and severe weather
conditions.
Collapse of the bridge also depends upon a phenomenon
called resonance. It is the phenomenon when a body vibrates
at its natural frequency & it shatters.
To avoid these types of failures today all new bridges
prototypes have to be tested in a wind tunnel before being
constructed.
14. QUALITY CONTROL IN SUSPENSION
CABLE
The main suspension cable in older bridges was often made from chain
or linked bars, but modern bridge cables are made from multiple strands
of wire. This contributes greater redundancy; a few flawed strands in the
hundreds used pose very little threat, whereas a single bad link or
eyebar can cause failure of the entire bridge.
Another reason is that as spans increased, engineers were unable to lift
larger chains into position, whereas wire strand cables can be largely
prepared in mid-air from a temporary walkway.
The cables are made of thousands of individual steel wires bound tightly
together. Steel, which is very strong under tension, is an ideal material
for cables; a single steel wire, only 0.1 inch thick, can support over half a
ton without breaking.
16. ADVANTAGES OVER OTHER BRIDGE TYPES
Longer main spans are achievable than with any other type of
bridge.
May be better able to withstand earthquake movements than
can heavier and more rigid bridges.
The center span may be made very long in proportion to the
amount of materials required, allowing the bridge to
economically span a very wide canyon or waterway.
It can be built high over water to allow the passage of very tall
ships.
17. LIMITATIONS COMPARED TO OTHER BRIDGE
TYPES
Considerable stiffness or aerodynamic profiling may be
required to prevent the bridge deck vibrating under high
winds.
The relatively low deck stiffness compared to other types of
bridges makes it more difficult to carry heavy rail traffic where
high concentrated live loads occur.
Under severe wind loading, the towers exert a large torque
force in the ground, and thus require very expensive
foundation work when building on soft ground.
18. LOAD DISTRIBUTION IN DIFFERENT TYPES OF BRIDGES
Cable-stayed bridge Beam bridge
tension
compression
Cantilever bridge
19. CONCLUSION
These are the pinnacles in modern days bridge technology.
Longer spans of up to 2000 ft-7000 ft is possible.
They are ideal for covering busy waterways such as Gulf,
Strait, Lake, etc.
These bridges are mainly meant for light & heavy roadways
rather than railways.
The main forces in a suspension bridge are tension in the
main cables and compression in the pillars.
